Japanese Laid-Open Utility Model Application No. 38402/1987 discloses a pressure control system in which a steering angular velocity is detected, and is utilized to increase a damping force or a spring constant of a suspension when the steering angular velocity and a vehicle speed respective exceed a predetermined value.
Japanese Laid-Open Patent Application No. 106,133/1988 discloses a pressure control system in which a turning pattern of a vehicle is determined on the basis of a steering angle and a steering angular velocity, and is utilized to modify a constant of proportionality or gain which is to be applied to a corrected suspension pressure which is determined in proportion to a lateral acceleration prevailing on the vehicle, and a required suspension pressure is calculated in accordance with the gain and the lateral acceleration of the vehicle to allow a pressure control valve to be energized so as to supply the required pressure to the suspension.
The pressure control systems mentioned above increase in accordance with an increasement of the steering angular velocity. It will be understood that the corrected suspension pressure changes responding to a change of the steering angular velocity, and consequently the corrected suspension pressure may be inclined to be excess or too little to cause a vertical oscillation of the car body to degrade a comfortability of an occupant or passenger.
Since the attitude (height) of the car body is not detected, and the pressure or the damping force is not adjusted depending on an actual attitude, namely, an unbalance of the attitude is not fed back in the pressure control systems, the pressure or the damping force of the suspension may be excessive or insufficient to maintain the car body in a desired attitude. The attitude of the car at a steering operation will be changed by a variety of a weight of the vehicle.
It is well known that a height of a car body is detected and a pressure of a suspension is adjusted for maintaining the height of the car body to a required height. However it will be understood that a deviation of the height of the car body from the required height arise, thereafter a required pressure of the suspension is calculated for decreasing the deviation. This means that an adjustment of the pressure has a delay from an alteration of the height of the car body. The delay may arise a fluctuation or hunching of the pressure of the suspension, which may cause a vertical oscillation of the car body to degrade a comfortability of an occupant or passenger.